Race and risk of schizophrenia in a US birth cohort: another example of health disparity?

Background Immigrant groups in Western Europe have markedly increased rates of schizophrenia. The highest rates are found in ethnic groups that are predominantly black. Separating minority race/ethnicity from immigration in Western Europe is difficult; in the US, these issues can be examined separately. Here we compared rates of schizophrenia between whites and African Americans and evaluated whether the association was mediated by socioeconomic status (SES) of family of origin in a US birth cohort. Methods Study subjects were offspring of women enrolled during pregnancy at Alameda County Kaiser Permanente Medical Care Plan clinics (1959-66) in the Child Health and Development Study. For schizophrenia spectrum disorders, 12 094 of the 19 044 live births were followed over 1981-97. The analysis is restricted to cohort members whose mothers identified as African American or white at intake. Stratified proportional hazards regression was the method of analysis; the robustness of findings to missing data bias was assessed using multiple imputation. Results African Americans were about 3-fold more likely than whites to be diagnosed with schizophrenia [Rate Ratio (RR) = 3.27; 95% confidence interval (CI): 1.71-6.27]. After adjusting for indicators of family SES at birth, the RR was about 2-fold (RR = 1.92; 95% CI: 0.86-4.28). Using multiple imputation in the model including family SES indicators, the RR for race and schizophrenia was strengthened in comparison with the estimate obtained without imputation. Conclusion The data indicate substantially elevated rates of schizophrenia among African Americans in comparison with whites in this birth cohort. The association may have been partly but not wholly mediated by an effect of race on family SES.